Examples of technique for examining the operational state of a machine on the basis of acoustic information includes a technique for performing examination by analyzing information given by a microphone installed in proximity to a machine to be monitored (See, e.g., JP-A 2003-279403 (KOKAI)). Another example includes a technique for using a non-fixed acoustic sensor such as a microphone provided in a cellular phone (See, e.g., JP-A 2008-33752 (KOKAI)).